Trailer backup aid speed limiting via braking

ABSTRACT

A trailer backup assist system for a vehicle reversing a trailer is provided herein. The system includes a brake system and a steering system of the vehicle. A controller is configured to output a brake torque request to the brake system and a steering command to the steering system, wherein the brake torque request and the steering command are each based at least in part on a trailer mass.

CROSS-REFERENCE TO THE RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/682,204, filed Apr. 9, 2015, and entitled “TRAILER BACKUPAID SPEED LIMITING VIA BRAKING,” now U.S. Pat. No. 9,744,972, the entiredisclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to systems for controllingvehicle parameters during vehicle guidance of a trailer, such as in atrailer backup assist system. In particular, various systems aredisclosed for controlling the speed or a vehicle during use of a trailerbackup assist system.

BACKGROUND OF THE INVENTION

Reversing a vehicle while towing a trailer can be challenging for manydrivers, particularly for drivers that drive with a trailer on aninfrequent basis or with various types of trailers. Systems used toassist a driver with backing a trailer can control various vehiclesystems to attempt to keep the speed of the vehicle below a limit wheresuch systems become unreliable, particularly at preventing the trailerfrom converging toward a jackknife angle or the like. Further advancesin such systems may be desired.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a trailer backupassist system for a vehicle reversing a trailer is provided. The systemincludes a brake system and a throttle sensor module outputting athrottle application signal. A controller outputs a brake torque requestto the brake system based at least in part on a trailer mass and thethrottle application signal.

According to another aspect of the present invention, a trailer backupassist system for a vehicle reversing a trailer is provided. The systemincludes a brake system and a steering system of the vehicle. Acontroller is configured to output a brake torque request to the brakesystem and a steering command to the steering system, wherein the braketorque request and the steering command are each based at least in parton a trailer mass.

According to another aspect of the present invention, a method ofreversing a trailer towed by a vehicle is provided. The method includesthe steps of determining a trailer mass, outputting a brake torquerequest to a brake system of the vehicle, and outputting a steeringcommand to a steering system of the vehicle if it's determined that thetrailer is being reversed along a straight path. The brake torquerequest and the steering command are each based at least in part on thetrailer mass.

These and other aspects, objects, and features of the present inventionwill be understood and appreciated by those skilled in the art uponstudying the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic depiction of an example vehicle and trailer;

FIG. 2 is a schematic depiction of the vehicle and the trailer of FIG. 1after reversing;

FIG. 3 is a schematic block diagram of a portion of a system forassisting the vehicle in reversing the trailer and includingfunctionality for limiting the speed of the vehicle;

FIG. 4 is a flowchart showing a method for limiting the speed of thevehicle, including by determining a road grade beneath the trailer ofFIGS. 1 and 2;

FIG. 5 is a schematic block diagram of a portion of an alternativesystem for assisting the vehicle in reversing the trailer and includingfunctionality for limiting the speed of the vehicle;

FIG. 6 is a flowchart showing an alternative method for limiting thespeed of the vehicle, including by dynamically adjusting a target speedof the system.

FIG. 7 is a schematic block diagram of a system for limiting the speedof a vehicle reversing a trailer based on a trailer mass, according toone embodiment;

FIG. 8 is a schematic block diagram of an alternative embodiment of thesystem shown in FIG. 7;

FIG. 9 is a schematic block diagram of a trailer backup assist systemaccording to one embodiment; and

FIG. 10 is a flowchart showing a method of reversing a trailer towed bya vehicle according to one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of description herein, the terms “upper,” “lower,” “right,”“left,” “rear,” “front,” “vertical,” “horizontal,” and derivativesthereof shall relate to the invention as oriented in FIG. 1. However, itis to be understood that the invention may assume various alternativeorientations, except where expressly specified to the contrary. It isalso to be understood that the specific devices and processesillustrated in the attached drawings, and described in the followingspecification are simply exemplary embodiments of the inventive conceptsdefined in the appended claims. Hence, specific dimensions and otherphysical characteristics relating to the embodiments disclosed hereinare not to be considered as limiting, unless the claims expressly stateotherwise.

Referring to FIGS. 1-3, reference numeral 10 generally designates avehicle that includes a system 12 for assisting vehicle 10 in backing upa trailer 14 coupled therewith. System 12 includes a brake system 16(FIG. 3) and a throttle sensor 22 (FIG. 3) that outputs a signal 24relating to an amount of throttle being applied. System 12 furtherincludes a controller 30 that estimates a road grade RG_(t) beneath thetrailer 14 and outputs a brake torque request 34 to the brake system 16based on the estimated road grade RG_(t) and the throttle applicationsignal 24.

Referring to FIG. 1, vehicle 10 is shown in an example scenario towingtrailer 14. An arm 18 of trailer 14 extends toward and couples trailer14 with vehicle 10 via a hitch (not shown) on the rear of vehicle 10. Inthis example, the vehicle 10 is reversing to move the trailer 14 fromthe position of FIG. 1 to the position of FIG. 2. In the example ofFIGS. 1 and 2, the vehicle 10 is a truck and the trailer 14 is a boattrailer and the reversing of vehicle 10 may be so as to move trailer 14into in a body of water at a boat lift, for example. The reversing maybe carried out using system 12, which is generally configured to assista driver of vehicle 10 in various ways in reversing vehicle 10 andtrailer 14. In one example, such a trailer backup assist system 12 canincludes both actions carried out by the driver of vehicle 10 as well asby system 12. In particular, the driver may initiate system 12 afterdriving vehicle 10 along a path to a desired location at which thereversing is to begin and placing vehicle 10 in reverse. Once system 12is activated, the driver may, for example, select a desired vehiclecurvature using an input device (such as a dedicated knob or, in someexamples, the steering wheel (not shown) of vehicle 10), whilesimultaneously controlling the longitudinal motion (i.e., speed) ofvehicle 10 using the throttle and brakes. In general, system 12 executesan operating routine to determine if the desired curvature can be safelyexecuted, which may mean that the desired curvature will maintain thehitch angle (i.e., an angle defined between the vehicle 10 and thetrailer 14 along a lateral plane at the point of coupling therebetween)below a “jackknife angle.” In general, a jackknife angle is described asan angle at which a maximum steering input in either direction will failto decrease the hitch angle. System 12 causes vehicle 10 to steerautomatically, such as by control of an electronic power assistedsteering (“EPAS”) system, to implement either the desired curvature or amodified curvature determined to be appropriate for preventing ajackknife condition, which may be determined by controller 30.

As mentioned, while system 12 is causing vehicle 10 to automaticallysteer to maintain an appropriate curvature, the driver may maintain thegeneral responsibility for controlling the longitudinal motion ofvehicle 10 using the throttle and brakes. Initially, such control shouldcause vehicle 10 to begin rearward motion. As vehicle 10 accelerates, itmay be generally the responsibility of the driver to maintain sufficientvehicle speed until a desired position is reached based on the curvaturealong which system 12 steers vehicle 10. Upon vehicle 10 reaching thedesired location, the driver may slow vehicle 10 by reducing throttleposition and applying brake torque before placing vehicle 10 in park anddeactivating system 12, at which point system 12 relinquishes control ofthe steering system.

The speed at which vehicle 10 travels while system 12 steers, however,can affect the ability of system 12 to avoid a jackknife condition orother adverse conditions. In particular, at higher vehicle speeds, thedynamics of the yaw rate of trailer 14 with respect to that of vehicle10 and, accordingly, the hitch angle may occur at a rate that is toofast for system 12 to react to avoid a hitch angle increase to or beyonda jackknife angle, as explained above. Accordingly, it may be desirablefor system 12 to be able to determine if the speed of vehicle 10 is ator is approaching a threshold at which system 12 may be unable toreliably control the hitch angle and to act to slow vehicle 10, ifnecessary. Further, it is noted that an EPAS system may only function tocontrol the steering of vehicle 10 while vehicle 10 is traveling below acutoff speed. Conversely, it may also be useful for system 12 to allowthe driver to utilize as much of the speed band as possible for purposesof flexibility and sense of control.

Accordingly, systems such as system 12 can include the ability withincontroller 30 to limit the speed of vehicle 10 by automatically applyingthe brakes, via an input to the vehicle brake system 16. A controller 30can be configured for speed limiting by the incorporation of aproportional-integral-derivative (“PID”) controller 42 to monitor thedifference between the vehicle speed and the target speed (suchdifference being designated a speed error) to request a brake torquerequest that will be sent to the brake system 16. This brake system 16in turn applies the brakes appropriately, which alters the vehicle speedand the speed error 40. For the purposes of speed limiting within asystem such as system 12, the desired response is a system that quicklylimits the vehicle speed to the target speed with very little overshoot.It is noted that minimizing overshoot overall, as opposed to simplyreducing overshoot quickly is desired, as the vehicle speed is desirablymaintained below the EPAS cutoff speed, for example, at all times, butflexibility through increased speed availability may also be desired.Accordingly, system 12 is configured to adjust to the outsidedisturbances of road grade and throttle apply input, which may be themost likely disturbances to significantly affect system 12 and theoverall speed of vehicle 10.

It is for this reason that system 12 uses feed forward tables based on aroad grade estimate 32 and the amount of throttle applied (“throttleapply”) to increase the robustness of the speed limiting controller foruse in system 12, as shown in FIG. 3. In particular, system 12 isconfigured such that controller 30 receives a vehicle speed input 28from speed detector 26, which is compared with a vehicle target speed38, which may be stored in memory 36, to arrive at a speed error signal40, which is input into PID controller 42 to arrive at an initial braketorque request signal 43. Simultaneously, system 12 can, using sensorassembly 20 (and possibly various other inputs, as described furtherbelow) estimate the road grade RG_(t) below trailer 14 to determine ifadditional brake torque is desirable. In general, such additional torquecan be added to the initial brake torque demand signal 43 to compensatefor an additional load on vehicle 10 by trailer 14 being on an increasedroad grade (i.e. an additional disturbance). An additional torque demandcan be correlated with variation in road grade RG_(t) in feed forwardtables stored in memory within controller 30 and can vary with trailer14 weight, brake system 16 parameters, desired response characteristicsof system 12 and the like.

Still further, controller 30 can receive a throttle apply input 24 fromthrottle sensor 22 and can determine a desired additional brake torquedemand corresponding to an amount of disturbance (if any) affectingsystem 12 due to an increased throttle application by the driver. Anadditional brake torque demand can be correlated with variation inthrottle in another feed forward table stored in memory 36 withincontroller 30 and can vary with engine characteristics, engine controlsettings, desired response characteristics of system 12, and the like.The feed forward gain added to the initial brake torque demand 43 canresult in a modified brake torque request 34 that can be output fromcontroller 30 to brake system 16 to slow vehicle 10 appropriately.

Referring to FIG. 4, a method 50 for controlling the speed of vehicle 10using the system 12, is described, along with example steps by whichcontroller 30 can estimate the road grade RG_(t) beneath trailer 14. Fora given vehicle towed, its associated road grade is, generally, a grade(or slope) of an area beneath the vehicle. Road grade can be expressedas a percentage of variation from a horizontal (zero) grade Hg. A roadgrade RG_(v) beneath vehicle 10 vehicle is a grade of an area of theroad beneath vehicle 10. A trailer road grade RG_(t) is a grade of aroad beneath the trailer 14. In the example of FIGS. 1 and 2, thetrailer road grade RG_(t) and the vehicle road grade RG_(v) are the samein FIG. 1 and different in FIG. 2. In FIG. 2, the trailer road gradeRG_(t) is greater than the vehicle road grade RG_(v).

As discussed above, vehicle 10 includes a sensor assembly 20 thatmonitors the vehicle road grade RG_(v). The assembly may includeaccelerometers, wheel speed sensors, and the like, that may monitor thevehicle road grade RG_(v) according to known methods. The vehicle 10further includes controller 30 coupled to the sensor assembly 20. Thecontroller 30 is a specialized controller and includes programming toestimate the trailer road grade RG_(t) based, in part, on the vehicleroad grade RG_(v). The controller 30 and sensor assembly 20 togetherprovide a trailer road grade assembly or system 12 for controlling thetrailer 14. Although described as road grade, it is to be understoodthat a traditional road is not required for there to be a road grade.Road grade refers generally to the area underneath a vehicle 10 whetherthat area is a road or that area is an off-road.

With continuing reference to FIG. 4, an example trailer road gradeestimating and speed control method 50 includes the step 52 ofestimating a first total mass of vehicle 10 and trailer 14. The step 52,thus, establishes a reference total mass. Notably, road grade RG_(t)beneath the trailer 14 is one of the variables used to estimate thetotal mass. In this example, changes in the total mass are attributed tochanges in the road grade RG_(t) beneath the trailer 14 relative to theroad grade RG_(v) beneath vehicle 10. Subsequently, at a step 54, themethod 50 estimates a second total mass of vehicle 10 and trailer 14.The step 54 occurs after movement in a reverse direction of the trailer14 such as from a first position (e.g. as shown in FIG. 1) to a second,different position (e.g. as shown in FIG. 2). At a step 56, the method50 calculates whether the first total mass is different than the secondtotal mass. If not, the method 50 returns to the step 54 and estimatesanother second total mass after more movement of the trailer 14.

If the second total mass is different than the first total mass, themethod 50 moves to step 58. At step 58 the difference between the firsttotal mass and the second total mass are used to calculate the roadgrade beneath the trailer 14. The method 50 may then correlate the roadgrade RG_(t) beneath trailer 14 with an additional brake torque demandin step 60 before feeding such additional brake torque demand to aninitial brake torque demand 43 from PID controller 42 in step 62, whichmay be effective to adjust the response of system 12 to an overspeedcondition, such as by automatically applying additional braking forcethat that which would otherwise be demanded by controller 30. Asdiscussed above, the method 50 can also feed forward values based ontorque apply to a brake torque demand from PID controller 42 to furtheradjust the final brake torque demanded by controller 30.

In a more specific example of the method 50, the step 52 includesestimating the total mass of the vehicle 10 and the trailer 14 using theequation:

${M_{c} = \frac{T_{pt} - T_{brk}}{R_{w}a_{x}^{s}}},$

-   -   where:    -   M_(c) represents the total unit mass of the vehicle 10 added to        the total mass of the trailer 14;    -   R_(w) represents the wheel radius;    -   a_(x) ^(s) represents an acceleration output from an        accelerometer;    -   T_(pt) represents a torque output from a powertrain of the        vehicle 10; and    -   T_(brk) represents a braking force output from a frictional        brake of the vehicle 10, the trailer 14, or both.

The above equation may be utilized to calculate total mass when, forexample, the vehicle 10 and trailer 14 are moving forward. If thevehicle 10 and the trailer 14 stray from forward movements and, forexample, begin to reverse, the example method 50 uses an alternativeformula to instantaneously estimate mass the of the vehicle 10 and thetrailer 14. The equation below shows an example formula thatdemonstrates relationships between variables when the vehicle 10 and thetrailer 14 are reversing:

${{\overset{\Cup}{M}}_{c} = {{M_{c} + {m_{tlr}g\frac{\left( {{\sin\mspace{14mu}\alpha_{r\; 2}} - {\sin\mspace{14mu}\alpha_{r\; 1}}} \right)}{a_{x}^{s}}}} = \frac{T_{pt} - T_{brk}}{R_{w}a_{x}^{s}}}},$

-   -   where:    -   {hacek over (M)}_(c) is the instantaneously estimated mass for        the vehicle 10 plus the trailer 14;    -   m_(tlr) is a mass of the trailer 14;    -   α_(r1) is a road grade under the vehicle 10;    -   g represents the gravity of earth; and    -   α_(r2) is the road grade under the trailer 14.

Changes in the instantaneously estimated mass {hacek over (M)}_(c) asthe vehicle 10 and the trailer 14 reverse are used to determine thegrade α_(r2) under the trailer 14. To derive the grade α_(r2) under thetrailer 14, the changes in the instantaneously estimated mass {hacekover (M)}_(c) are determined using the equation:RG _(load) ⁺ =m _(tlr) g(sin α_(r2)−sin α_(r1))=({hacek over (M)}_(c) −M_(c))a _(x) ^(s),

-   -   where RG_(load) ⁺ represents changes in load due to changes in        road grade beneath the vehicle 10 relative to the trailer 14.        The estimated road grade α_(r2) beneath the trailer 14, is then        determined using the equation:

${\alpha_{r\; 2} = \;{\arcsin\left\lbrack {\frac{\left( {{\overset{\Cup}{M}}_{c} - M_{c}} \right)a_{x}^{s}}{\left( {M_{c} - m_{trk}^{*}} \right)g} + {\sin\mspace{14mu}\alpha_{r\; 1}}} \right\rbrack}},$

-   -   where m*_(trk) is an estimated mass of the vehicle 10.        The mass of the vehicle 10 may be determined by weighing the        vehicle 10 or through some other technique, for example. A first        technique uses a constant value of the truck curb weight as        m*_(trk). Such a nominal value may be evaluated during or after        assembling the vehicle 10 at a factory and may be based on the        standard truck loading condition. In such an example, m*_(trk)        would remain constant. In a second example technique, m*_(trk)        may be an estimated mass based on the vehicle 10 mass for a        specific trip. This is useful when, for example, the vehicle 10        is periodically heavily loaded with cargo. This second technique        may provide a better estimate than the constant of the first        technique. The mass of the vehicle 10 for the second example        technique may be obtained using many different methods. An        example is to estimate mass of the vehicle 10 using active        suspension sensor. Deflection of the active suspension sensor at        a steady state tells the load variation on truck unit. The        estimated truck unit mass m*_(trk) in such an example will be        the truck curb weight plus the indicated load weight from the        suspension deflection.

In some examples, the estimated road grade can be used to calculate atotal road grade torque exerted on the vehicle 10. This total road gradetorque, represented as τ_(rgl), can be calculated using the equation:τ_(rgl)=(M _(c) −m* _(trk))g sin α_(r2) +m* _(trk) g sin α_(r1).The total road grade torque can, as described above, be used as afeedforward to derive a compensating torque to control the backup speedof the trailer 14 during an automatic backup procedure. As alsomentioned previously, additional feedforward compensating torque forbackup speed control can also be provided by the torque apply signal 24.

With respect to FIG. 5, another embodiment of a system 112 including acontroller 130 for assisting in maintaining the speed of vehicle 10below at maximum level when reversing a trailer 14, including undervarious forms of automated assistance from system 112, is described. Inparticular, controller 130 operates using a PID controller 142 in amanner similar to that described above with respect to FIG. 3, where PIDcontroller 142 provides a brake torque request 134 to brake system 116to attempt to slow vehicle 10 to reduce an error signal 140 between adetected speed 128 and a target speed 150. However, controller 130 canemploy a dynamic adjustment of the vehicle speed error to adjust thecontroller for steady state error or variation in overshoot. Such acontroller 130 can be used in a vehicle 10 that is not configured forproviding an estimate for the road grade below trailer 14 or can beincorporated into the above described system 12 to provide for robustovershoot control in a condition where a road grade estimate is notavailable (such as when the associated system has not yet accumulatedenough data to implement the above equations or the like).

System 112, in particular, dynamically adjusts the target vehicle speedto force the controller to come back to the desired steady state speedbased on the effect the adjustment on the target speed has on the speederror 140. In particular controller 130 includes the ability,illustrated in module 144 to receive as input the vehicle speed 128 fromspeed detector 126, which can be compared against a predeterminedcondition in the form of an initial (non-adjusted) target speed plus apredetermined maximum allowable error (which may be referred to as a“threshold speed”). Module 144 can then determine if the vehicle speedplus the maximum error is less than the non-adjusted target speed plusthe maximum error. If such a condition is present, module 144 canmaintain a “NoAdj” mode, in which the non-adjusted target speed isoutput from memory 136 for use in the error calculation for output ofthe error 140 to PID controller 142. If module 144 determines that thecurrent speed 128 plus the maximum error is greater than the targetspeed plus the maximum error, an adjusted (lowered) target speed can besubstituted for the predetermined target speed in determining the error140 provided to PID controller 142. A dynamically lowered error 140increases the brake torque request 134 output by controller 142, whichforces system 112 to lower the speed of vehicle 10 faster than it wouldusing the non-adjusted target speed.

FIG. 6 illustrates a method 166 by which system 112 can operate toattempt to regulate the speed of vehicle 10 during an assisted backupoperation. In particular, once initiated in step 168, system 112operates with controller 130 utilizing the actual, non-adjusted targetspeed to send to PID controller 142 (step 170 ). If, however, in step172 module 144 determines that the detected speed 128 of vehicle 10 isgreater than the target speed plus the maximum error, module 144 cancause controller 130 to transition to a “timer” state. As the maximumerror may be the maximum amount of error that is desired for the steadystate behavior of the controller, the timer state is used as a timeoutperiod to ensure that the overshoot of the controller does not affectthe steady state behavior by lowering the target speed in response tocontrollable overshoot. Accordingly the delay in step 174 may correlatewith the response time of PID controller 142 or other, relatedparameters of system 112. If the detected speed 128 is brought back downsuch that the speed 128 plus the maximum error is lower than thenon-adjusted target speed plus the maximum error before the delay instep 174 is over, then the system transitions back to the “NoAdj” state(step 170).

If the speed 128 is still such that speed 128 plus the maximum error isgreater than the non-adjusted target speed plus the maximum error afterthe delay 174 is over, then the system 112 in step 176 transitions to an“Adjustment” state. In such a state, the target speed 150 that is fedinto the PID controller 142 is substituted with a downward adjustedtarget speed 148 to pull the steady state speed back towards the actualtarget speed. If after another delay period (step 180) the speed isstill high (as determined in step 182), the adjusted target speed 148will be adjusted downward again (step 178). This will continue until thespeed 128 is within the determined range, as determined in step 182.

If the speed 128 drops such that the speed plus the maximum error isbelow the non-adjusted target speed plus the maximum, such as when thedriver is applying the brakes to slow down or the trailer 14 is nolonger on a higher road grade area than vehicle 10, the system 112transitions into a “slowrise” state 184. This state is designed toslowly raise the adjusted target speed 148 back up to the non-adjustedtarget speed at a controlled rate. The slow raising of the adjustedtarget speed 148 can help prevent undesirable behavior in the controller130. Finally, once the adjusted target speed 148 reaches thenon-adjusted target speed again, the system 112 reenters the “NoAdj”state (step 170) until system 112 is deactivated.

Referring to FIG. 7, another embodiment of a system 212 for limiting thespeed of a vehicle 10 based on a mass of trailer 14 is described. Thesystem 212 includes controller 230, which receives a vehicle speed input228 from speed detector 226. Vehicle speed input 228 is compared with avehicle target speed 238 stored in memory 236 to arrive at a speedsignal error 240. Speed signal error 240 is inputted into PID controller242 to ultimately arrive at brake torque request 234, which is outputtedfrom controller 230 to brake system 216 to slow vehicle 10appropriately. In the illustrated embodiment, PID controller 242 may bemodified directly based on the mass of trailer 14. According to oneembodiment, PID controller 242 is tuned for different trailer masses andthe gains of PID controller 242 are determined using lookup tables,which may be stored to a memory (e.g., 236) of controller 230.

Alternatively, with reference to FIG. 8, controller 230 may beconfigured as a feed forward controller where PID controller 242 outputsan initial brake torque request signal 243 that is added to a feedforward trailer mass gain 250 that may be supplied from trailer massestimation module 252 and helps compensate for variations in trailermass. The PID controller 242 may be nominally tuned and the value of thefeed forward trailer mass gain 250 will depend on the mass of trailer14. While not shown in FIG. 7 or 8, it should be appreciated that braketorque request 234 may include contributions from a road grade estimate,a throttle apply input, and/or other considerations described previouslyherein.

Referring to FIG. 9, controller 230 is shown in one embodiment of asystem 312 for assisting a vehicle 320 backing a trailer 325, alsoreferred to herein as a trailer backup assist system. Controller 230 maybe configured similarly to that shown in either FIG. 7 or 8 and includesa memory 332 having instructions 334 stored thereon. The instructions334 may be tangibly embodied as non-transitory computer readable mediumand are executable by a processor 336. The instructions are configuredto cause the processor 336 to carry out operations for generating asteering command 338 for a steering system 340 of the vehicle 320, whichmay include an electric power assisted steering (EPAS) system.Additionally, the instructions 334 are configured to cause the processor336 to carry out operations for generating a brake torque request 234 toa brake system 216 of the vehicle, as described previously herein.

The steering command 338 may be generated in part based on a hitch angleand a kinematic relationship determined between the vehicle 320 and thetrailer 325. In turn, a power-steering system controls steered wheels ofthe vehicle 320 based on the steering command 338. The steering of thevehicle 320 may be performed autonomously by the system 312 or manuallyvia an input device such as a rotatable knob or steering wheel of thevehicle 320. Additional information regarding trailer backup assistsystems and the generation of a steering command is found in U.S. PatentPublication No. 2014/0379219 to Rhode et al., entitled “TRAILER BACKUPASSIST CURVATURE CONTROL,” filed Sep. 10, 2014, the entire disclosure ofwhich is incorporated herein by reference.

According to one embodiment, the steering command 338 and the braketorque request 234 are each generated, at least in part, as a functionof a mass of the trailer 325. This may be achieved by modifying thegains of the controller 230 to compensate for variation in the mass ofthe trailer 325. Compensating for variation in trailer mass isparticularly advantageous because trailers of different masses willbehave differently while being reversed. For example, if backed along acurved trajectory, a lighter trailer will generally turn more quicklythan a heavier trailer. Thus, if trailer mass is not compensated for, adriver along with other vehicle occupants will encounter inconsistentexperiences when reversing trailers of different masses. To provide amore consistent experience, the gains of controller 230 may be increasedor decreased based on how heavy or light the trailer 325. In oneembodiment, the controller 230 may be tuned for a particular trailermass and the gains of the controller 230 may be increased if the trailer325 is heavier or decreased if the trailer 325 is lighter. In so doing,the driver and any other vehicle occupants are provided a moreconsistent experience whenever the vehicle 320 reverses a trailer 325,regardless of what the trailer mass is. As described herein, the gainsof the controller 230 may be determined using lookup tables.

In operation, the mass of the trailer 325 may be determined in a varietyof manners. According to one embodiment, a sensor system 345 operativelycoupled to the trailer 325 determines the mass of the trailer 325 andsends the corresponding trailer mass information 350 to the controller230. Additionally or alternatively, the mass of the trailer 325 may bedetermined by first weighing the trailer 325 (e.g., via a weigh scale)and then using a user-input device 352 to send the corresponding trailermass information 354 to the controller 230. The trailer mass information354 may be supplied to the controller 230 using a user-input device 352located within the vehicle 320 such as a touchscreen display of a centerconsole. It is also contemplated that the mass of the trailer 325 mayalso be supplied to the controller 230 using a portable electronicdevice configured to wirelessly communicate with the controller 230.Such electronic devices may include smartphones, tablets, and the like.Additionally or alternatively still, the mass of the trailer 325 may bedetermined based on trailer dynamics while the vehicle 320 and trailer325 are in motion, as described in U.S. Pat. No. 8,793,035 to Yu et al.,entitled “DYNAMIC ROAD GRADIENT ESTIMATION,” filed Jan. 7, 2013 theentire disclosure of which is incorporated herein by reference.

Referring to FIG. 10, a method 400 for assisting a vehicle 320 inreversing a trailer 325 is described with continued reference to thesystem 312 disclosed in FIG. 9. The method 400 may be embodied asinstructions 334 stored in memory 332 and executable by processor 336 ofcontroller 230. In describing the method 400, it is assumed that thevehicle 320 and trailer 325 are about to engage in a reversing maneuver.For example, the method 400 may be initiated at step 410 when a driverof the vehicle 320 shifts into reverse or otherwise communicates his orher intent to perform a reversing of the trailer 325. At step 420, themass of the trailer 325 is determined. As described herein, there areseveral ways in which the trailer mass can be computed such as, but notlimited to, using sensor system 345, weighing the trailer mass andinputting the trailer mass to the system 312 via user-input device 352,or via calculations related trailer dynamics while the trailer 325 is inmotion. Next, at step 430, the controller 230 checks whether a straightbackup maneuver is being performed, that is, whether the trailer 325 isbeing reversed in a substantially straight line. If so, the controller230 generates a brake torque request as a function of the trailer massat step 440. As described herein, the brake torque request is sent tothe brake system 216 to control the speed in which the vehicle 320 andthe trailer 325 are being reversed. The brake torque request mayadditionally or alternatively be a function of other considerationsdescribed herein such as, but not limited to, a road grade estimateand/or a throttle application signal. If it is determined at step 430that a straight backup maneuver is not being performed, the controller230 generates a brake torque request along with a steering command, eachbeing a function of trailer mass, as illustrated in steps 450 and 460,respectively. As described herein, the steering command is sent to thesteering system 340 to control steered wheels of the vehicle 320 whilethe trailer 325 is being reversed. As further described herein, thesteering command may also be a function of a hitch angle and a kinematicrelationship determined between the vehicle 320 and the trailer 325. Itshould be appreciated that the controller 230 may modify the braketorque request and the steering command (when applicable) as needed solong as the trailer 325 is being reversed. Once the vehicle 320 and thetrailer 325 are parked (e.g., the driver places the vehicle 320 inpark), trailer backup assist functionality may come to an end at step470.

Accordingly, trailer backup assist system has been described herein thatis configured to generate a brake torque request for limiting the speedof a vehicle and a steering command for controlling a steering systemresponsible for automatically steering the vehicle while the vehiclereverses the trailer. The brake torque request and the steering commandmay each be based at least in part on a mass of the trailer. In thismanner, a more consistent driving experience is achieved by virtue ofthe trailer backup assist system being able to compensating for trailermass during a backing maneuver.

It will be understood by one having ordinary skill in the art thatconstruction of the described invention and other components is notlimited to any specific material. Other exemplary embodiments of theinvention disclosed herein may be formed from a wide variety ofmaterials, unless described otherwise herein.

For purposes of this disclosure, the term “coupled” (in all of itsforms, couple, coupling, coupled, etc.) generally means the joining oftwo components (electrical or mechanical) directly or indirectly to oneanother. Such joining may be stationary in nature or movable in nature.Such joining may be achieved with the two components (electrical ormechanical) and any additional intermediate members being integrallyformed as a single unitary body with one another or with the twocomponents. Such joining may be permanent in nature or may be removableor releasable in nature unless otherwise stated.

It is also important to note that the construction and arrangement ofthe elements of the invention as shown in the exemplary embodiments isillustrative only. Although only a few embodiments of the presentinnovations have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multiple partsor elements shown as multiple parts may be integrally formed, theoperation of the interfaces may be reversed or otherwise varied, thelength or width of the structures and/or members or connector or otherelements of the system may be varied, the nature or number of adjustmentpositions provided between the elements may be varied. It should benoted that the elements and/or assemblies of the system may beconstructed from any of a wide variety of materials that providesufficient strength or durability, in any of a wide variety of colors,textures, and combinations. Accordingly, all such modifications areintended to be included within the scope of the present innovations.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions, and arrangement of the desired andother exemplary embodiments without departing from the spirit of thepresent innovations.

It will be understood that any described processes or steps withindescribed processes may be combined with other disclosed processes orsteps to form structures within the scope of the present invention. Theexemplary structures and processes disclosed herein are for illustrativepurposes and are not to be construed as limiting.

It is also to be understood that variations and modifications can bemade on the aforementioned structure without departing from the conceptsof the present invention, and further it is to be understood that suchconcepts are intended to be covered by the following claims unless theseclaims by their language expressly state otherwise.

We claim:
 1. A trailer backup assist system for a vehicle reversing atrailer, comprising: a brake system; and a controller configured to:generate a speed signal error by comparing a stored vehicle target speedwith a vehicle speed input received from a speed detector; generate abrake torque request based on the speed signal error and a trailer mass;and output the brake torque request to the brake system; wherein thecontroller is further configured to calculate an estimated road grade ofa surface on which the trailer is positioned; wherein the estimated roadgrade is determined by estimating a first total mass of the vehicle andtrailer and comparing the first total mass to a second total mass of thevehicle and trailer that is estimated after movement of the trailer in areverse direction from a first position to a second position; whereinthe estimated road grade is based on the difference between the firstand second total mass; and wherein the brake torque request is furtherbased on the estimated road grade and a throttle application signal froma throttle sensor.
 2. The trailer backup assist system of claim 1,wherein the trailer mass is obtained via user input.
 3. The trailerbackup assist system of claim 1, wherein the trailer mass is obtainedvia sensors disposed on the trailer.
 4. The trailer backup assist systemof claim 1, wherein the trailer mass is estimated based on trailerdynamics while the trailer is in motion.
 5. The trailer backup assistsystem of claim 1, wherein the controller comprises aproportional-integral-derivative controller configured to receive thespeed signal error and generate the brake torque request, and whereinthe proportional-integral-derivative controller is tuned for differenttrailer masses and the gains of the proportional-integral-derivativecontroller are determined using lookup tables.
 6. The trailer backupassist system of claim 1, wherein the controller is further configuredto output a steering command to a steering system of the vehicle,wherein the steering command is based at least in part on the trailermass.
 7. A trailer backup assist system for a vehicle reversing atrailer, comprising: a brake system of the vehicle; and a controllerconfigured to: generate a speed signal error from a stored vehicletarget speed and a vehicle speed input received from a speed detector;generate an initial brake torque request signal from the speed signalerror; generate a brake torque request from the initial brake torquerequest signal and a feed forward gain that is based on trailer mass andsupplied from a trailer mass estimation module; and output the braketorque request to the brake system; wherein the controller is furtherconfigured to calculate an estimated road grade of a surface on whichthe trailer is positioned; wherein the estimated road grade isdetermined by estimating a first total mass of the vehicle and trailerand comparing the first total mass to a second total mass of the vehicleand trailer that is estimated after movement of the trailer in a reversedirection from a first position to a second position; wherein theestimated road grade is based on the difference between the first andsecond total mass; and wherein the brake torque request is further basedon the estimated road grade and a throttle application signal from athrottle sensor.
 8. The trailer backup assist system of claim 7, whereinthe trailer mass is obtained via at least one of user input and sensorsdisposed on the trailer.
 9. The trailer backup assist system of claim 7,wherein the trailer mass is estimated based on trailer dynamics whilethe trailer is in motion.
 10. A method of controlling the speed of avehicle towing a trailer, comprising the steps of: receiving a vehiclespeed input from a speed detector; generating a speed signal error froma stored vehicle target speed and the vehicle speed input; generating aninitial brake torque request signal from the speed signal error;generating a brake torque request from the initial brake torque requestsignal, a feed forward gain that is based on trailer mass and suppliedfrom a trailer mass estimation module, an estimated road grade of asurface on which the trailer is positioned, and a throttle applicationsignal from a throttle sensor; and outputting the brake torque requestto a brake system of the vehicle; wherein the estimated road grade isdetermined by estimating a first total mass of the vehicle and trailerand comparing the first total mass to a second total mass of the vehicleand trailer that is estimated after movement of the trailer in a reversedirection from a first position to a second position; and wherein theestimated road grade is based on the difference between the first andsecond total mass.
 11. The method of claim 10, wherein the trailer massis obtained via at least one of user input and sensors disposed on thetrailer.
 12. The method of claim 10, wherein the trailer mass isestimated based on trailer dynamics while the trailer is in motion. 13.The method of claim 10, wherein the initial brake torque request signalis generated by a proportional-integral-derivative controller using thespeed signal error as input.
 14. The method of claim 10, furthercomprising the step of outputting a steering command to a steeringsystem of the vehicle, wherein the steering command is based on thetrailer mass, a hitch angle, and a kinematic relationship between thevehicle and the trailer.